1. Field of the Invention
This invention relates to an automatic tracking control device and more particularly to a tracking control device suited for a recording/reproducing apparatus such as a helical scanning type video tape recording/reproducing apparatus (hereinafter called a VTR) in which a moving element laterally moves a reproducing head relative to a recording track formed on a recording medium and a control circuit controls the moving element to cause the head to trace recording tracks on the recording medium.
2. Description of the Prior Art
Various types of automatic tracking control devices of the above-stated type have been proposed. Some of these devices have already been put to practical use in VTR's.
In an automatic tracking control device of this type, an electro-mechanical transducer element such as a bimorph plate or the like using a piezo-electric or electrostriction element (hereinafter called an actuator) has been employed as the above-stated moving element. Generally, it is desirable to reduce the range over which the actuator must move the head while the head's tracking of the recording tracks remains satisfactory. A proposed method for accomplishing this involves controlling the rotation of a capstan with a signal obtained by integrating a drive voltage signal applied to the actuator. According to this method, the mean value of the drive voltage applied to the actuator can be brought closer to zero and the degree of deflection of the actuator, i.e., the head's moving range, can be decreased. This method is quite advantageous because the residual distortion of the actuator can be reduced and the adverse effect of the non-linearity of the actuator can be avoided.
However, there are other important factors that must also be taken into consideration including the touch characteristic between the reproducing head and the recording tape and a tracking characteristic relative to the disturbance of the tape travel load. Therefore, the prior art methods of controlling the rotation of the capstan with a signal obtained by integrating the control voltage applied to the actuator require a large integration time constant. This results in a low response speed for capstan control and this has presented a problem in that respect.
There exist special reproducing modes in which a recorded signal is reproduced at a tape travel speed different from the recording speed, such as fast forward/backward reproducing (searching), slow reproduction, etc. In those modes it is possible to reproduce the recording without a noise bar in the reproduced picture by adding a voltage of a triangular wave form, one which corresponds to the tape travel speed, to a tracking signal when scanning the tape surface with the reproducing head before the tracking signal is applied to the actuator. In this instance, however, the actuator is required to move the head over a much greater range than in a normal reproducing operation. Depending on the reproducing tape travel speed, the head moving range extends from scores of microns to several hundred microns. Therefore, this method has presented a problem with respect to the build-up characteristic of the tracking operation during switch-over from one tape travel speed to another.